thE stuDy oF thE EnD-pErmiAn mAss ExtinCtion is hinDErED By All oF thE Following ExCEpt ______.
A．thE lACk oF ExpEriEnCED rEsEArChErs
B．lACk oF ACCEss to southErn ChinA
C．lACk oF rElEvAnt roCk sAmplEs
D．lACk oF wEll-prEsErvED Fossils